1. Field of the Invention
The present invention relates to a substrate processing apparatus useful for plating a substrate or processing a substrate by dipping a substrate in a processing liquid.
The present invention also relates to a substrate processing method and apparatus useful for a pre-plating treatment which may be carried out before electroless plating for the formation of an interconnects-protective layer on the exposed surfaces of embedded interconnects of a conductive material, such as copper, silver or gold, embedded in fine interconnect grooves formed in the surface of a substrate, such as a semiconductor wafer.
Further, the present invention relates to a substrate holding device suitable for use in processing the processing surface of a substrate with a plating solution or other processing liquid, a substrate processing apparatus incorporating the substrate holding device, and a method for attaching/detaching a substrate to and from a substrate holding device.
2. Description of the Related Art
As a process for forming interconnects in a semiconductor substrate, a so-called “damascene process”, which comprises embedding a metal (electric conductor) into trenches for interconnects and contact holes, is coming into practical use. According to this process, aluminum, or more recently a metal such as silver or copper, is embedded into trenches for interconnects and contact holes previously formed in an interlevel dielectric. Thereafter, an extra metal is removed by performing chemical mechanical polishing (CMP) so as to flatten a surface of the substrate.
In a case of interconnects formed by such a process, for example copper interconnects formed by using copper as an interconnect material, embedded interconnects of copper have exposed surfaces after the flattening processing. In order to prevent thermal diffusion of such interconnects (copper), or to prevent oxidation of such interconnects (copper) e.g. during forming thereon an insulating film (oxide film) under an oxidizing atmosphere to produce a semiconductor substrate having a multi-layer interconnect structure, it is now under study to selectively cover the exposed surfaces of interconnects with an interconnects-protective layer (cap material) composed of a Co alloy, a Ni alloy or the like so as to prevent thermal diffusion and oxidation of the interconnects. Such an interconnects-protective layer of a Co alloy, a Ni alloy or the like can be produced e.g. by performing electroless plating.
As shown in FIG. 1, for example, fine grooves 4 for interconnects are formed in an insulating film 2 of SiO2 or the like which has been deposited on a surface of a substrate W such as a semiconductor wafer. A barrier layer 6 of TaN or the like is formed on the entire surface, and then copper plating, for example, is carried out onto the surface of the substrate W to fill the grooves 4 with copper and deposit copper film on the surface of the substrate W (damascene process). Thereafter, CMP (chemical mechanical polishing) is carried out onto the surface of the substrate W so as to flatten the surface of the substrate, thereby forming interconnects 8 composed of a copper film in the insulating film 2. Thereafter, an interconnects-protective layer (cap material) 9 composed of a Co—W—P alloy film is formed e.g. by electroless plating selectively on the surfaces of interconnects (copper film) 8 to protect interconnects 8 (cap plating process).
A common electroless plating method for the selective formation of the interconnects-protective layer (cap material) 9 of the Co—W—P alloy film on the surfaces of interconnects 8 generally involves the following process steps: First, the substrate W such as a semiconductor wafer, which has undergone the CMP treatment, is immersed in an acid solution (first treatment liquid) e.g. of 0.5M H2SO4 at the solution temperature of e.g. 25° C. for e.g. one minute to remove CMP residues, such as copper, remaining on a surface of an insulating film 2. After cleaning the surface of the substrate W (pre-cleaning process) with a cleaning liquid (second treatment liquid) such as ultrapure water, the substrate W is immersed in a mixed solution (first treatment liquid), e.g. of 0.005 g/L PdCl2 and 0.2 ml/L HCl, at the solution temperature of e.g. 25° C. for e.g. one minute to adhere Pd as a catalyst to the surfaces of interconnects 8, thereby activating the exposed surfaces of interconnects 8. Next, after cleaning the surface of the substrate W with a cleaning liquid (second treatment liquid) such as ultrapure water (first pretreatment process), the substrate W is immersed in a solution (first treatment liquid) containing e.g. 20 g/L of Na3C6H5O7.2H2O (sodium citrate) at the solution temperature of e.g. 25° C., thereby carrying out neutralization treatment of the surfaces of interconnects 8. Thereafter, after washing the surface of the substrate W (second pretreatment process) with ultrapure water (second treatment liquid), the substrate W is immersed in a Co—W—P plating solution at the solution temperature of e.g. 80° C. for e.g. 120 seconds, thereby carrying out selective electroless plating (electroless Co—W—P cap plating) onto the activated surfaces of interconnects 8. Thereafter, the surface of the substrate W is cleaned with a cleaning liquid such as ultrapure water (plating process). The interconnects-protective layer 9 composed of a Co—W—P alloy film is thus formed selectively on the surfaces of interconnects 8 to protect interconnects 8.
A substrate processing apparatus (plating apparatus), which includes a number of devices for carrying out the above-described plating step and various incidental pretreatments to the plating step and cleaning steps, is required to carry out the various processing steps securely with a good product quality. In addition, there is a demand for making the whole apparatus compact and reducing the apparatus cost.
As described above, when forming an interconnects-protective layer (cap material) composed of a Co—W—P alloy film by electroless plating, a catalyst-imparting treatment for imparting a catalyst, for example Pd, to the surfaces of interconnects is carried out in advance. Further, removal of CMP residues, e.g. copper, remaining on an insulating film, which treatment is necessary for preventing an interconnects-protective layer from being formed on the insulating film, is carried out usually by using an inorganic acid, such as H2SO4 or HCl. On the other hand, an electroless plating solution is generally an alkaline solution. Accordingly, it is necessary to carry out a neutralization step immediately before plating to stabilize the plating process.
In order to securely carry out uniform plating in the necessary area of the surface of a substrate after performing the pre-plating process, it is necessary to securely impart a catalyst only to that area (plating area) in the catalyst-imparting treatment, and effect a neutralization treatment, etc. over the whole area to which a catalyst has been imparted.
In conventional plating apparatuses, however, a pre-cleaning treatment (chemical cleaning), which is carried out prior to a catalyst-imparting treatment, a catalyst-imparting treatment and a cleaning treatment (neutralization treatment) after the catalyst-imparting treatment, are generally carried out by using devices having the same construction. Accordingly, the respective areas of a substrate to be subjected to the pre-cleaning (chemical cleaning), to the catalyst-imparting treatment and to the cleaning (neutralization) after the catalyst-imparting treatment are basically the same. With such a conventional apparatus, due to a device error, a variation in positioning of a substrate when it is held, etc., there is a case where that area of the substrate to which a catalyst will be imparted is not entirely pre-cleaned (with a chemical) or a case where the area of the substrate to which the catalyst has been imparted is not entirely cleaned (neutralized) after the catalyst-imparting treatment, whereby plating cannot be effected securely in the necessary area of the substrate surface.
As a method for carrying out a stable and uniform plating (e.g. electroless plating) of a substrate or carrying out a stable and uniform pretreatment of a substrate, a dip processing method in which a substrate is dipped in a processing liquid so as to bring the processing liquid into contact with the processing surface of the substrate, has conventionally been employed. With respect to such dip processing method, removal of gas bubbles remaining on the processing surface of a substrate is the most important technical problem to be solved for carrying out stable and uniform various processings. In this regard, when dipping a substrate in a processing liquid in parallel (horizontal) to the liquid surface, gas bubbles adhere to the processing surface of the substrate, which adversely affect the processing. As a method for removing gas bubbles, a method has been proposed in which a substrate in a tilted position is immersed in a processing liquid and the substrate is then returned to the horizontal position to carry out processing.
In the case of the method of tilting a substrate, however, a tilting mechanism must be provided in a substrate holding apparatus. This makes the apparatus complicated and increases the weight of the apparatus and, in addition, impedes reduction of the apparatus cost.
The state of a substrate after the catalyst-imparting treatment in the above-described first pretreatment step has a great influence on the plating on the later processing step. Accordingly it is necessary to carry out a stable and secure catalyst-imparting treatment. As a method for carrying out stable and secure pretreatments of a substrate, such as a catalyst-imparting treatment, a dip processing method in which the substrate is dipped in a processing liquid so as to bring the processing liquid into contact with the processing surface, has conventionally been employed. In carrying out the processing of a substrate by dipping the substrate in a processing liquid, removal of gas bubbles adhering on the processing surface of the substrate is essential for the stable and uniform processing of the substrate. However, adequate measures for removal of gas bubbles have not been taken.
In a substrate processing apparatus for carrying out the above-described plating and the like, a substrate holding device, which holds a substrate by attracting the back surface of the substrate, is generally employed. Such a substrate holding device includes a plate-like attracting head and holds a substrate by attracting by vacuum the back surface of the substrate to a suction pad mounted to the lower surface of the attracting head. Various processings, such as plating, are carried out by bringing various processing liquids, such as a plating solution, into contact with the processing surface of the substrate thus held in the substrate holding device.
A suction pad is generally designed to attract by suction substantially the entire back surface of a substrate. The vacuum attraction of substantially the entire back surface of the substrate (nearest possible to the edge) is to best prevent adhesion of a processing liquid to the back surface of the substrate.
With such attracting means as a suction pad in which the entire inside space becomes vacuum, however, when holding a substrate by vacuum attraction, the substrate can deform largely from the center to the peripheral region due to the vacuum attraction force, whereby uniform plating cannot be effected and, in the worst case, the substrate can be broken. Further, the pad of a suction pad usually also functions as a sealing member, and therefore a rubber material is commonly employed. A rubber material, due to a change in the quality with time, etc., becomes sticky to a substrate. Accordingly, a substrate attracted to a suction pad is hard to detach from it, obstructing attachment/detachment of the substrate.